The present invention relates to a dielectric porcelain material used in the micro-wave frequency region. More particularly, the invention relates to such a material used in frequencies higher than X-band, and which effectively demonstrates high no-load Q and stable thermal properties.
ZrO.sub.2 -SnO.sub.2 -TiO.sub.2 and BaO-TiO.sub.2 systems, and those systems partially substituted with other elements, or composite materials having a controlled thermal coefficient obtained by combining positive dielectric porcelains or glass with negative TiO.sub.2, are heretofore well-known. However, their dielectric constants are as high as from 30 to 40. On the other hand, with the increasing use of high frequency regions and from the viewpoint of workability, materials with dielectric constants of about 10, rather than those with high constants as above described, have become of interest in the manufacture of porcelain substrates for dielectric resonators.
Alumina porcelains are known to have small dielectric constants. However, the thermal coefficients of aluminia porcelains which are as high as .+-.60 ppm/.degree.C. have inhibited their practical applications.
In Japanese Patent Application No. 32113/84, materials are disclosed having compositions falling in the quadrilateral area defined in the Al.sub.2 O.sub.3 -CaO-TiO.sub.2 ternary composition diagram in the application by connecting the following points:
______________________________________ Al.sub.2 O.sub.3 CaO TiO.sub.2 ______________________________________ point A 0.94 0.04 0.02 B .81 .14 .05 C .81 .02 .17 D .94 .01 .05 ______________________________________
The materials are manufactured by combining alumina sinterings of thermal coefficients (hereinafter denoted .tau.f) which have negative large-absolute values such as -60 ppm/.degree.C., high no-load Q, small dielectric loss at high frequencies and excellent thermal conductivity, mechanical strength and chemical stability properties, with CaO+TiO.sub.2 -derived calcium-titanate materials of large positive .tau.f values. It has been desired, however, to further improve the .tau.f and no-load Q of the materials which are the invention of Japanese Patent Application No. 32113/84.
The principal object of the present invention is, therefore, to provide a dielectric porcelain material for use in the micro-wave frequency region that has improved .tau.f and no-load Q, and in particular, .tau.f and no-load Q which are improved over those of the materials of Japanese Patent Application No. 32113/84.